This invention relates to a magnet pump, in which a magnet coupling between a drive and a driven magnet facing each other rotationally drives an impeller in a pump chamber for a pumping operation and, more particularly, to improvements in a front and a rear side thrust bearing, particularly the rear thrust bearing member for supporting the thrust acting on a driven rotor portion including an impeller.
A prior art magnetic pump of this type has a structure as shown, for instance, in FIG. 3. The well-known magnet pump 1 as shown in FIG. 3 comprises a front casing having a suction port 3 extending in the axial direction as shown by axis line X--X and a discharge port 4 extending circumferentially, an impeller 6 rotationally disposed in the pump chamber 2 and having a front side portion (i.e., right side in the Figure) facing the suction port 3, a cylindrical rear casing with a bottom cooperating with a front casing 5 to enclose the pump chamber 2 liquid tight, a driven rotor 10 disposed outside a rear casing 7, having a ring-like drive magnet 8 and receiving a rotational drive torque from a drive motor (not shown) disposed in a pump body 9, a driven rotor 12 disposed in the rear casing 7, having a ring-like driven magnet 11 facing and forming a magnet coupling with the drive magnet 8 via the rear casing and rotatable in unison with the impeller, and a spindle 14 secured at the distal end thereof to the bottom 7a of the rear casing 7 via an integral boss 13 projecting from the bottom 7a and having an extended end portion projecting axially for rotatably supporting the driven rotor 12 on the extended end portion via a sleeve-like bearing 15.
In the above well-known magnet pump 1, the rotation of the drive rotor 10 causes rotational driving of the driven rotor 12 to cause rotation of the impeller 6, thus causing fluid to be pumped to flow into the pump chamber 2 through the suction port 3 as shown by the arrow and be sent out through the discharge port 4 as shown by the arrow. In this pumping operation, the fluid in the pump chamber 2 partly flows as a circulating flow into the depth of the rear casing 7. In the circulating flow, the fluid flows into the frictional contact portions 15a defined between the sleeve-like bearing 15 integral with the driven rotor 12 and the spindle 14 from the rear end side of the bearing 15 as shown by dashed line arrows to come out to the front end side and pass through a central communication hole 16 provided in the impeller 6, thereby providing a cooling effect to suppress increased heat generation by the friction of the frictional contact portions 15a and also providing a lubricating action. In the frictional contact portions 15a, a fluid passage groove is formed, which is a helical groove or like a spline.
During the pumping operation, a negative pressure prevails on the front side of the impeller 6 that faces the suction port 3, while the driven rotor section including the driven rotor 12 and the impeller 6 normally receives a thrust in the direction toward the suction port 3, i.e., in the direction toward the front. Thus, ring-like front thrust bearing 17 is provided in the front casing 5 for supporting the thrust, and a mouth ring 18 provided on the side of the impeller 6 is in frictional contact with the front thrust bearing 17.
Further, a thrust may act on the driven rotor section in the direction opposite to the direction toward the suction port 3, i.e., in the rearward direction. This results from vibration of the driven rotor section in the thrust direction while the driven rotor portion remains rotating, which is caused when the pump is operated idly or abnormally due to trapping of air, or a like cause. Thus, a rear thrust bearing member 19 for supporting the rearward thrust acting on the driven rotor section is provided on a boss 13 around the spindle 14, so that the rear end of the sleeve-like bearing 15 is in frictional contact with the rear thrust bearing member 18 in the event of the generation of a rearward thrust.
As noted above, the sleeve-like bearing is brought to a state with its rear end in frictional contact with the rear thrust bearing member in the event of the idling operation of the pump or an abnormal operation thereof, such as air trapping. At this time, frictional heat is generated in the frictional contact portions, and this poses a problem. More specifically, the rear thrust bearing member, unlike the front thrust bearing member, is provided in the depth of the rear casing therefore, diffusion of the frictional heat is inferior, and when the temperature is increased, the bearing parts are seized. Particularly, where the rear casing or like enclosure member is a synthetic resin molding, the heat has an adverse effect of causing damage to these parts due to fusing. Further, when the rear end of the sleeve-like bearing is brought into frictional contact with the rear thrust bearing member, the circulating flow entering the frictional contact portions defined around the spindle generates heat and generate circulation failure, thus making the problem more significant.
To solve the problem, it has been proposed to provide a heat isolation structure adopting a heat insulating material such as to surround the frictional contact portions of the rear thrust bearing or the like. In this case, a cost increase due to the provision of the heat insulation structure is inevitable. In addition, since the heat insulation material prevents diffusion of heat, the frictional contact portions are quickly elevated in temperature even by a short period of idling, and what is commonly called heat shock is liable to be generated by priming fluid supplied into the pump chamber immediately afterwards.